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Dr. R. H. Traquair — On Drepanaspis. 



then, is an explanation of the imperforate pit seen on the dorsal 

 surface. For it is now quite clear that this appearance is caused 

 by one of the dorsal plates being squeezed down upon the aforesaid 

 thickened ring-like margin of the round opening in the sensory 

 plate, which accordingly shows through, although the opening itself 

 is on the ventral surface, as shown in Fig. 2, x. 



Fig. 1. Brepanaspis Gemilndenensis, Schl. Eestored outline of the dorsal aspect, 



the surface ornament omitted, and the tail twisted round so as to show the 

 caudal fin in profile, m.cl. median dorsal plate ; p.l. postero-lateral plates ; 

 r. rostral plates. 



Consequently the object x is an actual opening which perforates 

 a special plate (sensory) belonging to the ventral aspect of the 

 head, and the appearance of a pit on the dorsal aspect is due to 

 pressure during fossilization, and should be deleted from the 

 restoration, as I have done in Fig. 1. 



That this opening, which, though perforating a plate belonging 

 to the ventral surface, lies just within the lateral margin of the head, 



